1. Field of the Invention
The present invention relates to a pipe mounting structure of an expansion valve suitable for use in a refrigeration cycle.
2. Description of the Related Art
A refrigeration cycle in an automotive air conditioner generally includes a compressor for compressing a circulating refrigerant, a condenser for condensing the compressed refrigerant, an expansion valve for throttling and expanding the condensed liquid refrigerant and delivering the resulting spray of refrigerant, and an evaporator for evaporating the misty refrigerant to cool the air in a vehicle interior by evaporative latent heat. The expansion valve is, for example, a thermostatic expansion valve that senses the temperature and the pressure of the refrigerant on the outlet side of the evaporator, and opens or closes a valve section so that the refrigerant delivered from the evaporator has a predetermined degree of superheat, to control the flow rate of the refrigerant to be delivered to the evaporator.
The expansion valve has a body in which a first passage through which the refrigerant flowing from the condenser toward the evaporator passes and a second passage through which the refrigerant having returned from the evaporator passes to be delivered to the compressor are formed. The first passage includes a valve hole, and a valve element disposed facing the valve hole. The valve element moves toward and away from the valve hole to adjust the flow rate of the refrigerant flowing toward the evaporator. A power element that senses the temperature and the pressure of the refrigerant flowing through the second passage and operates in response to the sensed temperature and pressure is provided at one end of the body. The drive force of the power element is transmitted to the valve element via an elongated shaft. The shaft extends through an insertion hole formed in a partition that divides between the first passage and the second passage, and is slidably supported in the insertion hole. One end of the shaft is connected to the power element, and the other end thereof extends through the valve hole and is connected to the valve element (refer to Japanese Unexamined Patent Application Publication No. 2013-242129, for example).
In such an expansion valve, a Karman vortex may be generated on the downstream side of the shaft while the refrigerant flowing through the second passage passes along the shaft, and abnormal noise (hereinafter also referred to as “Karman vortex sound”) may be caused thereby. This is considered to be due to resonance caused when the eigenvalue (natural frequency) of a space where the shaft is present in the second passage and the frequency of the Karman vortex correspond to each other (coincidence of eigenvalues). An approach to such a problem may be to provide a design so that the eigenvalue of the space and the frequency of the Karman vortex are shifted from each other. Even if such an approach is carried out, however, the eigenvalues may become coincident again as a result of a change in the eigenvalue of the space caused by a change in a joint of the expansion valve, for example. Furthermore, since the frequency of a Karman vortex also changes with the flow rate of the refrigerant, the eigenvalues may become coincident as a result of such a change. This may result in generation of Karman vortex sound.